The invention relates to magnetic material which comprises a magnetic phase which is composed mainly of crystalline RE The invention also relates to a magnet which is manufactured from this magnetic material.
Magnetic material of the type mentioned above is known from, inter alia, Ferromagnetic Materials, Edition E.P. Wohlfarth and K.H.J. Buschow, Elsevier Science Publishers B.V., Volume 4, pages 131-209, 1988. More in particular, on page 150 of said literature reference eleven RE.sub.2 Fe.sub.17 compounds are represented (FIG. 11, x=1), wherein RE denotes the rare earth metals Ce, Pr, Nd, Sm, Gd, Dy, Er, Tm, Yb, Th and Y. These compounds have a hexagonal crystal structure of the Th.sub.2 Ni.sub.17 type or the much related rhombohedral structure of the Th.sub.2 Zn.sub.17 type. By virtue of the relatively high Fe content these compounds are interesting, in principle, for use as hard magnetic material in permanent magnets. The said Figure, however, shows that these RE.sub.2 Fe.sub.17 compounds do not have a uniaxial magnetic anisotropy. Thus, they are unsuitable for use as permanent magnetic material.
One of the objects of the invention is to provide a magnetic material on the basis of RE.sub.2 Fe.sub.17 compounds which has a relatively high uniaxial anisotropy at room temperature. A further object of the invention is to provide a permanent magnet which is manufactured from this material.
This object is achieved by a material of the type mentioned in the opening paragraph, which is characterized according to the invention in that interstitial C is dissolved in the magnetic phase, in a quantity which is sufficiently large to provide the magnetic material with a uniaxial magnetic anisotropy, and in that RE consists of at least 70 at.% of the rare earth metal Sm.
It has been found that the crystalline structure of the RE.sub.2 Fe.sub.17 material hardly changes when interstitial C is dissolved therein. The RE.sub.2 Fe.sub.17 C.sub.x compounds also have a hexagonal structure of the Th.sub.2 Ni.sub.17 type or the Th.sub.2 Zn.sub.17 type. Further, the volume of the unit cell of RE.sub.2 Fe.sub.17 C exceeds that of the unit cell of RE.sub.2 Fe.sub.17 by only approximately 2%. An important consequence hereof is that no appreciable magnetic dilution occurs. Magnetic dilution is disadvantageous because it leads to a reduction of the saturation magnetization. Magnetic dilution would occur, in particular, when in the RE.sub.2 Fe.sub.17 lattice C replaces one or more Fe atoms. Applicants have indications that dissolved C rather brings about an increase of the saturation magnetization.
Further, it has been found that at room temperature the uniaxial magnetic anisotropy of the C-containing RE.sub.2 Fe.sub.17 compounds which do not contain a considerable quantity of Sm is negligibly small. Compounds of said type such as, for example, Gd.sub.2 Fe.sub.17 C or Y.sub.2 Fe.sub.17 C generally exhibit a so-called in-plane anisotropy, i.e., at room temperature the anisotropy direction of the material is not uniaxial, but extends perpendicularly to the crystallographic C-axis. This renders them unsuitable for use as hard magnetic material for permanent magnets.
It is to be noted that in J. Less-Common Met. 142 349-357 (1988), a description is given of a number of Nd.sub.2 Fe.sub.17 C.sub.x compounds. Said compounds have an in-plane anisotropy which even exceeds, that of Nd2Fe.sub.17.